DESCRIPTION (Adapted from the Investigator's Abstract) The broad objectives of this project are to advance our understanding of the neural and hormonal mechanisms by which animals learn the sounds used for vocal communication during a sensitive period of development. Songbirds are one of the few groups of animals other than humans that learn to produce specific vocalizations based on the experience of hearing sounds in their auditory environment. Zebra finch males learn to produce a specific vocal pattern by hearing that acoustic pattern early in development, and by using auditory feedback of their own self-produced vocalizations in order to match their vocal motor commands to that acoustic pattern. As adults, males use auditory feedback to maintain their previously learned song pattern in a highly stereotyped form, and are apparently unable to learn new vocalizations. The system is sexually dimorphic: males sing and females do not, and song-control brain regions in males are several-fold larger than in females. (1) We will test whether de-stabilization of stereotyped song patterns caused by removal of auditory feedback re-induces neural and behavioral plasticity characteristic of the sensitive period for vocal learning. (2) We will assess specific relationships between brain structure and function by separately lesioning two different neural circuits that are important for vocal production during the sensitive period for vocal learning. (3) We will examine the intrinsic and synaptic physiology of song-control neurons in a brain slice preparation in order to characterize patterns of functional communication between neurons. (4) We will manipulate the growth of specific song-control brain regions in males and females using neurotrophic growth factors and measuring the resultant effects on vocal learning and behavior. In the aggregate, these experiments will advance our understanding of neural and behavioral mechanisms that contribute to sensitive periods for vocal learning, and have general implications for relationships between development and learning, and sexual differentiation of the nervous system. The results of these experiments will also bear importantly on hypotheses of vocal learning in humans, and may have immediate application to problems of speech perception and production.